How to Give Your Pet an Insulin Injection

Quick answer

Draw up the dose your vet prescribed, lift a fold of loose skin over the back or side, insert the needle into the base of the fold parallel to the body, press the plunger smoothly, then praise and treat.

Use a new needle every time and a different spot every time. A re-used needle is blunt, which causes the pet more distress, and risks infection. Injecting the same spot repeatedly builds scar tissue and fatty lumps that stop insulin absorbing properly.

Check your syringes match your insulin's concentration — U40 and U100 syringes are not interchangeable. If you are unsure a dose went in, ask your vet rather than repeating it.

The first injection is the one most owners dread. The needles are tiny, the injection goes just under the skin where there are few nerve endings, and most pets barely react, especially with a treat waiting. Your vet or nurse should demonstrate on your own pet first; this guide reinforces what they show you.

Preparing the dose

Wash your hands, then mix the insulin exactly as your vet showed you and as its package leaflet says — products differ, and some must be shaken while others are rolled. Draw up the exact prescribed dose, tap any large air bubbles to the top and push them out, and double-check the number against your vet's instruction. Every time.

Use the right syringe for your insulin. Insulins come in different strengths — for example 40 units per ml or 100 units per ml — and each needs syringes marked for that strength. Using the wrong syringe gives the wrong dose without you noticing. If you're not sure your syringes match your insulin, check with your vet or pharmacist before the next injection.

Giving the injection

The usual spot is the loose skin over the back or side. Gently lift a fold of skin into a "tent" between finger and thumb, insert the needle into the base of the tent parallel to the body, press the plunger smoothly, and withdraw. Then — and this part matters just as much — warm praise and the after-injection treat, so the whole thing becomes a positive ritual rather than an ordeal.

Move the spot every time

Use a genuinely different spot each injection rather than a favourite one. Injecting into the same place builds scar tissue and fatty lumps under the skin, and insulin absorbs less well from those areas — a common and easily missed reason a pet's diabetes will not settle. Working around the diagram above in a regular rotation is enough.

Needles are single-use

Used needles and syringes go into a sharps bin — a rigid, puncture-proof container, never household waste, and never loose in a bin bag where someone could be injured. Your vet or pharmacy can supply one and will tell you how to return it when it is full; many councils also run a collection service. Ask your practice what they want you to do locally, as arrangements vary.

The rule that matters most

If you're not sure the full dose went in — a "fur shot" that sprayed onto the coat, a wriggle mid-injection:

Making it stress-free

Routine and calm are everything: same times, same relaxed spot, treat ready before you start, and your own nerves kept easy — pets read our tension. Many owners inject while their pet eats and the pet barely notices. Within a couple of weeks it's as ordinary as brushing their coat.

Mello logs every injection with its time and who gave it, so nobody has to remember at 7am, and it can remind you when a dose is due. Treat a reminder as a prompt rather than a guarantee: it rings on one phone, and a phone on silent or out of battery will not ring at all.

If a dose is missed or you are unsure whether it went in, read what to do next. If your pet will not eat, see the food refusal guide, and keep the diabetic emergencies guide handy.

Sources

The pages below were each opened and checked before being listed here, and anything that could not be opened was left off rather than guessed at.

• Caninsulin 40 IU/ml: package leaflet (Vm 06376/4083) — Veterinary Medicines Directorate, Defra, revised February 2026. That U-40 syringes must be used with this product, that sites are alternated daily, and the injection site relative to the midline.

Which syringe you need is decided by which insulin your pet is on, and the two are not interchangeable. If you are not certain which you have, see insulin types and syringes in the UK before you draw anything up.

• 2018 AAHA Diabetes Management Guidelines for Dogs and Cats — Journal of the American Animal Hospital Association 54(1):1–21, 2018. Two rules verbatim: syringes are single use, and a U-40 syringe goes with U-40 insulin and a U-100 syringe with U-100 insulin.
• ISFM Consensus Guidelines on the Practical Management of Diabetes Mellitus in Cats — Journal of Feline Medicine and Surgery 17(3):235–250, 2015. That veterinary insulins in common use are 40 U/ml while many others are 100 U/ml, and that repeated puncture leaves a vial open to contamination.
• Caninsulin 40 IU/ml Suspension for Injection — MSD Animal Health UK, prepared October 2024. The difference this page insists on: the vial is inverted to mix, while a VetPen cartridge is shaken thoroughly — and neither is used if clumps remain.